In recent years, an augmented reality technology (AR technology) has drawn attention, which combines virtual objects or various kinds of information as additional information and as electronic information with a real environment (or a portion thereof), and presents the combined information. To achieve the augmented reality technology, a head-mounted display has been examined as a device for presenting visual information, for example. The head-mounted display is expected to be applied for job support in the reality environment. For example, the head-mounted display may be applied for providing of route guidance information and of technical information to the engineer who performs maintenance, for example. In particular, the head-mounted display is very convenient since the hands are free. In addition, even when enjoying a video or an image while moving outdoors, the user can see the video or the image and an external environment at the same time. Therefore, the user can move smoothly.
For example, JP 2006-162767 A discloses a virtual image display device (image display device) in which a virtual image optical system changes a two-dimensional image formed by an image forming device into an enlarged virtual image such that the observer can observe the virtual image.
As illustrated in FIG. 34, which is a conceptual diagram, an image display device 100′ includes an image forming device 111 including a plurality of pixels arranged in a two-dimensional matrix, a collimating optical system 112 that converts light emitted from the pixels of the image forming device 111 into parallel light, and an optical device (light guide unit) 120 on which the parallel light converted in the collimating optical system 112 is incident, in which the light is guided, and from which the light is emitted. The optical device 120 includes a light guide plate 121 in which incident light propagates while being totally reflected and from which the light is emitted, a first deflection unit 130 (for example, a single-layer light reflecting film) that reflects light incident on the light guide plate 121 so as to be totally reflected in the light guide plate 121, and a second deflection unit 140 (for example, a multi-layer light reflecting film having a multi-layer structure) that allows the light, which has propagated in the light guide plate 121 while being totally reflected, to be emitted from the light guide plate 121. For example, when an HMD is formed by the image display device 100′, the weight and the size of the device can be reduced. Refer to the image display device according to Example 1 illustrated in FIG. 1 with regard to reference numerals denoting the other components illustrated in FIG. 34 are.
In addition, for example, JP 2007-94175 A discloses a virtual image display device (image display device) using a hologram diffraction grating in which a virtual image optical system changes a two-dimensional image formed by an image forming device into an enlarged virtual image such that the observer can observe the virtual image.
As illustrated in FIG. 35, which is a conceptual diagram, an image display device 300′ basically includes an image forming device 111 that displays an image, a collimating optical system 112, and an optical device (light guide unit) 320, which light displayed on the image forming device 111 is incident on, and which guides the light to a pupil 21 of the observer. Here, the optical device 320 includes a light guide plate 321, and first and second diffraction grating members 330 and 340 that are reflective volume hologram diffraction gratings provided on the light guide plate 321. Light emitted from each pixel of the image forming device 111 is incident on the collimating optical system 112, and a plurality of parallel light with different incident angles to be incident on the light guide plate 321 is generated by the collimating optical system 112 and is then incident on the light guide plate 321. The parallel light is incident on a first surface 322 of the light guide plate 321, and is then emitted therefrom. Meanwhile, the first diffraction grating member 330 and the second diffraction grating member 340 are attached to a second surface 323 of the light guide plate 321 that is parallel to the first surface 322 of the light guide plate 321. Refer to the image display device according to Example 3 with reference to FIG. 12 with regard to reference numerals denoting the other components illustrated in FIG. 35.
When images are displayed on the image display devices 100′ and 300′, the observer can view the displayed image and an external image in an overlapped manner.
However, sufficiently high contrast may not be given to the image observed by the observer when the brightness of a surrounding environment in which the image display devices 100′ and 300′ are located is very high or depending on the content of the displayed image.
For example, JP 2004-101197 A discloses means for solving the problem. In the technology disclosed in JP 2004-101197 A, a liquid crystal shutter controls the quantity of incident light incident on the pupil of the observer from an outside.